Hoppers are widely used on docks to receive material from the conveyor belts of self unloading vessels. Strict environmental laws and regulations dictate that dust created through the transfer of cargo from ship to shore must be controlled.
Self unloading vessels are generally fitted with an unloading boom of some 50 feet to 260 feet in length which swings out over the dock area. The end of this boom is positioned over a receiving hopper which guides the material flowing in its trajectory from the end of an endless belt conveyor to a second conveyor belt positioned under the shore based hopper.
Cargoes of particulate matter such as ore, coal, cement clinker, stone, grain, phosphate rock, gypsum, etc. create dust as they fall in their trajectory from the end of the ship's boom and strike the sides of the receiving hopper.
Various means have heretofore been proposed for controlling the escape of dust as particulate matter is discharged from a discharge chute therefor. In most instances, the discharge chute and the receptacle for the particulate matter are relatively static, or move in a predictable manner. In the discharge of cargo from a ship, there are predictable changes as the draft of the ship is reduced, but to these there must be superimposed unpredictable changes resulting from the variable effect of winds, tides and wave action on the ship.
In accordance with one proposal, a flexible pipe is used to connect between the boom end and the hopper. However, it is found that the abrasion and impact forces from the particulate matter severely limits the life of such pipe. Moreover, where such pipe is wire wound, there may be considerable hold up of particulate matter between the coils, which either results in contamination of a succeedingly discharged cargo, or necessitates a time consuming cleaning operation. Additionally, flexible pipes as have been heretofore proposed do not permit adequate movement of the discharge chute in vertical planes, as is required in connection with the unloading of ships.
In accordance with other proposals, canvas shrouds have been draped over the end of the boom, to surround the hopper, but this does not permit the requisite degree of movement between the boom and the hopper. Various types of hanging skirts have also been used to contain dust. They are usually hung from the end of the boom and surround the falling material in its path between boom end and hopper. A fine water spray is sometimes used in conjunction with this skirt but moisture content of many cargoes is critical and added water is not acceptable.
In accordance with still further proposals, the receiving hopper is sometimes constructed in such a manner as to form a box-like structure around the end of the boom, and is often fitted with suction devices to filter the dust laden air from the structure. Such hoppers are generally efficient, but require large capital investments. A danger exists however, due to the fact that such box-like structures are generally made of steel, and any unexpected movement of the boom may well result in damage to the boom or hopper or both.
It is then an object of the present invention to provide improved apparatus for containing dust. It is a further object of the invention to provide such apparatus which is suitable for use in the discharge of cargo from ships, particularly self unloading ships.